PTC. The moment arm would be at least 15 

 feet, which would mean bending moments of 

 15 feet X 20,000 pounds or 300,000 foot- 

 pounds. Design of a cylinder to handle such 

 loads would be difficult. This concept was 

 considered unfeasible for the PTC. 



Rope-Net Catch (Fig. 12.30): The simplest 

 concept in which the principle of pulling the 

 vehicle snug against a member fixed relative 

 to the ship manifested itself in the rope-net 

 catch concept. Two or three outriggers are 

 used to lay a large rope net on the ocean 

 surface. A strength cable is then threaded 

 through the center of the net and used to 

 pull the vehicle up. Once caught in the net, 

 the weight of the outriggers keeps a taut 

 downward pull on the vehicle and prevents 

 undesired motion as the vehicle is removed 

 from the sea. The strength cable is reeved 

 through a sheave on the ship's boom. 



The major problem with this concept is the 

 inherent untidiness and unpredictability of 

 the net. Also, fragile appendages on the vehi- 

 cle could easily be damaged. 



Fig 12 30 Rope net calch. 



The foregoing delineates the wide variety 

 of methods and concepts available to launch/ 

 retrieve a submersible at sea. 



It would be tidy to say that system "X" is 

 the best and therefore recommended over all 

 others. But, as we have seen, the variety in 

 submersible weights, dimensions and config- 

 urations is myriad, and what might work for 

 one will not work for another. Doerschuk et 

 al. found that no one concept was right for 

 handling the PTC and they proceeded to take 

 the most desirable features of several and 

 combine them, as was feasible, into a suita- 

 ble system. This procedure might well be the 

 best solution to present and future handling 

 problems. But no matter what the selection 

 procedure is based upon, one should not ex- 

 pect an ultimate arrangement; because the 

 sea has a whimsical personality and, as Usry 

 concluded: "There will always be an element 

 of danger when handling such loads at sea 

 and no computer is going to suddenly reveal 

 a shining solution free of compromises." 



LIFT HOOKS 



Though seemingly a simple problem, the 

 selection of lift hooks is of extreme impor- 

 tance and — as demonstrated by DS-4000^s 

 helicopter hook failure with pilot and crew 

 aboard and a consequent 8-foot drop — it can 

 be a critical choice. The proper selection calls 

 for a hook that is quickly and easily attached 

 for lifting and will not jump out of its re- 

 straint as the submersible is lifted or jerked 

 about. For launching, the requirements are 

 that it will not fail or release accidentally 

 and can be quickly released when desired. 



Pelican Hook (Fig. 12.31): This type of hook 

 is in general use. It is cheap, rugged and 

 quick to attach. Problems can arise, however, 

 when the vehicle and support craft are in 

 dissimilar motion, and it is sometimes quite 

 difficult to obtain sufficient slack to hook up. 

 Further, a diver is required to detach the 

 hook, and, as the submersible is wet and 

 slippery, the diver must hold on with one 

 hand, detach the hook and then avoid its 

 wild swinging until it is lifted clear. It can be 

 a difficult proposition. 



U.S. Navy Safety Hook (Fig. 12.32): This 

 hook has been adapted for use by the DEEP- 

 STAR series of submersibles. It has been 

 tested to 44 tons and cannot be opened as 



615 



